Detecting an automotive lamp outage with a current sensor is well known in the art. The current sensor generally comprises a low ohmic resistor in series with the lamp. The resistance value of the resistor limits the amount of heat dissipated and energy lost through the resistor. When the voltage drop across the resistor exceeds a threshold voltage level as compared by a voltage comparator, an output is generated which drives an automotive circuit that monitors the operation of the lamp. The comparator is required because the low voltage level obtained with the resistor is not sufficient to drive the automotive circuit. However, the resistor generates an excessive amount of heat when the lamp is powered and functioning. In addition the plurality of resistor type current sensors, required to detect outages in the many lamps of an automobile, are typically grouped on a circuit board. The cumulative heat build up from the resistor type current sensors on the circuit board results in unnecessary failures and energy losses.
A ferrite core with a coil and a Hall effect transducer has also been used as a method for sensing a flow of current. The coil is connected in series with a device, for example an automotive lamp, so that when power is applied to the device a current passes through the coil. The current in the coil, which is wrapped around the ferrite core, generates a magnetic field which is transferred through the ferrite core to the Hall effect transducer, which senses magnetic flux above a threshold level and produces an electrical output. However, ferrite cores generally consist of nonmetallic, ceramic-like compounds and are restricted to certain shapes and sizes. The ferrite core of a size adequate for sensing an automotive lamp current occupies a prohibitive amount of circuit board space. Also, the ferrite core is easily fractured and requires additional hardware for mounting on a circuit board. Although the ferrite core type sensor dissipate less heat than the resistor type current senors, the ferrite core type sensor is not suitable to be employed in sensing the operation of an automotive lamp.
Materials with a high magnetic permeability have long been used as a core for a coil. However, a magnetic field generated by a coil having such a core has not been previously configured so as to be suitable for employment in sensing the operation of an automotive lamp.